Why does rigid body physics not work in objects created by an object instancer? (Animation nodes)
First, you are setting their locations explicitly using the Transforms Output node, so the simulation obviously won't take effect. Second, objects need to be linked to the RigidBodyWorld collection, so you can use the following expression:

[collection.objects.link(obj) for obj in objects if obj.name not in collection.objects]


So, your node tree should be as follows: